This invention relates to disposable food contact compatible microwaveable containers having at least one micronodular surface including cups, trays, soufflxc3xa9 dishes, lids, plates, bowls, and related articles of manufacture useful for preparation, storage, delivery, and serving of food, wherein convenience and low cost are of paramount importance. Nevertheless, appearance and tactile characteristics of the plate, container, etc., are important for consumer preference. The suitability of these disposable articles of manufacture for microwave cooking, or heating of food, has an important place in today""s marketplace. Both the commercial and retail market components need an aesthetically pleasing microwaveable, disposable, rigid and strong container, plate, or cup, and related article of manufacture. This invention is directed to economically meeting that need and provides a container or plate comprising an extruded sheet of a polyolefin selected from the group consisting of polypropylene, polypropylene polyethylene copolymer or blend, or a mixture of these coupled with mica or a similar platy inorganic mineral.
These disposable microwaveable containers and plates exhibit (a) a micronodular surface on the food contact side of the plate or container, and (b) a melting point of no less than about 250xc2x0 F., said container or plate being dimensionally stable and resistant to grease, sugar, and water at temperatures up to at least 220xc2x0 F. and exhibiting sufficient toughness to be resistant to cutting by serrated polystyrene flatware. Microwaveable and disposable containers and plates having all the aforementioned properties are not known in the prior art. In U.S. Pat. No. 5,377,860, assigned to assignee of the present patent application, a double shell food container is disclosed. The composition and properties of the container differ from the present invention since a polyolefin/mica composition is not suggested or disclosed and the container does not have the thermal properties or the micronodular surface of the containers disclosed herein. The containers disclosed in European Patent Application D544,429A1 do not suggest or disclose a container which can meet the thermal properties and have the desirable micronodular surface of the container of the present invention.
Microwaveable, disposable, rigid, strong and food contact compatible containers and plates have been prepared. These disposable and microwaveable articles of manufacture exhibit (a) a micronodular surface on the side coming in contact with the food; and (b) a melting point of not less than 250xc2x0 F., suitably 250xc2x0 F. to 330xc2x0 F. These microwaveable, food contact compatible containers and plates are dimensionally stable and resistant to grease, sugar, and water at temperatures of at least 220xc2x0 F. and are of sufficient toughness to be resistant to cutting by serrated polystyrene flatware. These containers, in the form of disposable lunch (8.75 inch) and dinner plates (10.25 inch), exhibit a SSI rigidity of at least 200 grams per 0.5 inch at a basis weight of about 130 lbs. per 3000 square foot ream. At a basis weight of about 200, SSI rigidity is about 300 grams per 0.5 inches; and at a basis weight of about 360, SSI rigidity is about 700 grams. The containers and plates of this invention answer a long felt need for products which can withstand the severe conditions of a microwave oven when common foods such as beans and pork, pancakes with syrup, pepperoni pizza, and broccoli with cheese are microwaved during food cooking and reconstituting processes. When the polyolefin is combined with mica, these containers and plates exhibit a micronodular surface on one or both sides usually on the side coming in contact with the food.
As shown in Example 9 and Table 12, competing commercial polystyrene type plates cannot withstand the high temperatures generated in the microwave oven during food contact and either significantly warped or deformed when the aforementioned food products were placed on them. Under the usual microwaving conditions with high grease content foods, the prior art plates tend to deform and flow to the point where parts of the plate became adhered to the inside of the microwave oven. For disposable plates and containers, appearance and feel are important attributes. The micronodular surface of the plates and containers of this invention where mica is used in combination with polypropylene or polypropylene polyethylene copolymers or blends tend to give these products the pleasing appearance and feel of stoneware or a pottery-like look. Another significant property of the containers and plates of this invention is their cut resistance. These rigid articles of manufacture are of sufficient toughness to be resistant to cutting by serrated polystyrene flatware. In normal usage they are also resistant to cutting by regular metal flatware.